PSYC 1010-(MODULES 17-19) SENSATION + PERCEPTION.docx

PSYC 1010 REBECCA JUBIS
SENSATION & PERCEPTION
MODULE 17
SENSATION: the process by which our sensory receptors and nervous system receive
and represent stimulus energies from our environment
PERCEPTION: the process of organizing and interpreting sensory information, enabling
us to recognize meaningful objects and events
BOTTOM –UP PROCESSING: analysis that begins with the sensory receptors and
works up to the brain’s integration of sensory information
TOP-DOWN PROCESSING: information processing guided by higher-level mental
processes, as when we construct perceptions, draw on our experience and expectations
- All our senses
 Receive sensory stimulation, often using specialized receptor cells
 Transform that stimulation into neural impulses
 Deliver the neural information to our brain
TRANSDUCTION: conversion of one form of energy into another. In sensation, the
transforming of stimulus energies, such as sights, sounds, and smells into neural impulses
our brain can interpret
PSYCHOPHYSICS: the study of relationships between the physical characteristics of
stimuli, such as their intensity, and our psychological experience of them
ABSOLUTE THRESHOLD: the minimum stimulation needed to detect a particular
stimulus 50% of the time
SIGNAL DETECTION THEORY: a theory prediction how and when we detect the
presence of a faint stimulus (signal) amid the background stimulation (noise), Assumes
there is no single absolute threshold and that detection depends partly on a person’s
experience, expectations, motivation and alertness
SUBLIMINAL: below one’s absolute threshold for conscious awareness
PRIMING: the activation, often unconsciously, of certain associations, thus predisposing
one’s perception, memory or response
 In a typical experiment, the image or word is quickly flashed, then replaced by a
masking stimulus that interrupts the brain’s processing before conscious perception - Much of our information processing occurs automatically, out of sight, off the
radar screen of our conscious mind
DIFFERENCE THRESHOLD: the minimum difference between two stimuli required
for detection 50% of the time. We experience the difference threshold as a just noticeable
difference (jnd)
WEBER’S LAW: the principle that, to be perceived as different, two stimuli must differ
by a given percentage (rather than a given amount)
SENSORY ADAPTION: diminished sensitivity as a consequence of constant
stimulation
 When we are constantly exposed to a stimulus that does not change, we become less
aware of it because our nerve cells fire less frequently
o Why, then, if we stare at an objection without flinching, does it NOT vanish from
sight? – Unnoticed by us, our eyes are always moving; the continual flitting from
one spot to another ensures that stimulation on the eyes’ receptors continually
changes
o BENEFIT: freedom to focus on informative changes in our environment without
being distracted by background chatter
o We perceive the world not exactly as it is, but as it is useful for us to perceive it
PERCEPTUAL SET: a mental predisposition to perceive one thing and not another
- Through experience we form concepts, or schemas, that organize and interpret
unfamiliar information
- A given stimulus may trigger radically different perceptions, partly because of
our differing perceptual set, but also because of the immediate context
- Perceptions are influenced, top-down, not only by our expectations and by the
context but also by our emotions and motivations
- Perceptual bias energizes our going for it; our motives also direct our perception
of ambiguous images
 Emotions also colour our social perceptions MODULE 18
VISION
a) The Stimulus Input: Light Energy
WAVELENGTH: the distance from the peak of one light or sound wave to the peak or
the next. Electromagnetic wavelengths vary from the short blips of cosmic rays to the
long pulses of radio transmission
HUE: the dimension of colour that is determined by the wavelength of light; what we
know as the colour names blue, green etc.
INTENSITY: the amount of energy in a light or sound wave, which we perceive as
brightness or loudness, as determined by the wave’s amplitude
b) The Eye
- Light enters the eye through the cornea, which protects the eye and bends light to
provide focus
PUPIL: the adjustable opening in the center of the eye through which light enters
IRIS: a ring of muscle tissue that forms the coloured portion of the eye around the pupil
and controls the size of the pupil opening
LENS: the transparent structure behind the pupil that changes shape to help focus images
on the retina
RETINA: the light-sensitive inner surface of the eye, containing the receptor rods and
cones plus layers of neurons that begin the processing of visual information
ACCOMMODATION: the process by which the eye’s lens changes shape to focus near
or far objects on the retina
- The retina doesn’t ‘see’ the a whole image, rather its millions of receptor cells convert
particles of light energy into neural impulses and forward those to the brain
 There, the impulses are reassembled into a perceived, upright seeming image
i. The Retina
RODS: retinal receptors that detect black, white, and gray; necessary for peripheral and
twilight vision, when cones don’t respond
CONES: retinal receptor cells that are concentrated near the center of the retina and that
function in daylight or in well-lit conditions. The cones detect fine detail and give rise to
color sensations  The light energy trigger chemical changes that would spark neural signals, activating
nearby bipolar cells
o Bipolar cells in turn would activate the neighboring ganglion cells --> optic nerve
OPTIC NERVE: the nerve that carries neural impulses from the eye to the brain
BLIND SPOT: the point at which the optic nerve leaves the eye, creating a ‘blind’ spot
because no receptor cells are located there
FORVEA: the central focal point in the retina, around which the eye’s cones cluster
 Each one transmits to a single bipolar cell that helps relay the cone’s individual
message to the visual cortex
o Rods share bipolar cells with other rods, sending combined messages
c) Visual Information Processing
- Information processing begins in the retina’s neural layers which are actually brain
tissue that migrate to the eye during fetal development; help encode and analyze
sensory information
 The same sensitivity that enables retinal cells to fire messages can lead
them to misfire
ii. Feature Detection
FEATURE DETECTION: nerve cells in the brain that respond to specific features of
the stimulus, such as shape, angle, or movement
 These cells pass tis information to other cortical areas, where teams of cells (supercell
clusters) respond to more complex patterns
o For biologically important object and events, we have a ‘vast visual encyclopedia’
distributed as specialized cells
o These cells respond to one type of stimulus
o Other cells integrate this information and fire only when the cues collectively
indicate the direction of someone’s attention and approach
iii. Parallel Processing
PARALLEL PROCESSING: the processing of many aspects of a problem
simultaneously; the brain’s natural mode of information processing for many functions,
including vision. Contrasts with the step-by-step (serial) processing of most computers
and of conscious problem solving
 Separate visual systems for perception and action illustrate dual processing- the two-
track mind
d) Color Vision
- Color like all aspects of vision, resides not in the object but in the theatre of our
brains, as evidenced by our dreaming in color YOUNG- HELMHOLTZ TRICHROMATIC (THREE-COLOR) THEORY: the
theory that the retina contains three different color receptors- one most sensitive to red,
one to green, one to blue- which, when stimulated in combination, can produce the
perception of any color
 Most people with color-deficient vision are not actually ‘colorblind’
o They simply lack functioning red-or green-sensitive cones, or sometimes both
o Their vision is monochromatic (one-color) or dichromatic (two-color) instead of
trichromatic, making it impossible to distinguish the red and green
- Hering, found a clue in afterimages, where trichromatic theory lacked evidence of
leaving some parts of the colour vision
 Colour processing occurs in two stages
1) The retina’s red, green, and blue cones respond in varying degrees to different
color stimuli (Young- Helmholtz trichromatic theory)
2) Their signals are then processed by the nervous system’s opponent-process cells
(Hering’s theory)
OPPONENT- PROCESS THEORY: the theory that opposing retinal processes (red-
green, yellow-blue, white-black) enable color vision. For example, some cells are
stimulated by green and inhibited by red; others are stimulated by red and inhibited by
green
VISUAL ORGANIZATION
GESTALT: an organized whole. Gestalt psychologists emphasized our tendency to
integrate pieces of information into meaningful wholes
 In perception, the whole may exceed the sum of its parts
o Our brain does more than register information about the world; we filter
incoming information and construct perceptions
a) Form Perception
i. Figure & Ground
o In our eye-brain system, our first perceptual task is to perceive any object
(figure) as distinct from its surroundings (ground)
FIGURE-GROUND: the organization of the visual field into objects (figures) that stand
out from their surroundings (ground)
ii. Grouping
o We must also organize the figure into a meaningful form
GROUPING: the perceptual tendency to organize stimuli into coherent groups  Proximity; we group nearby figures together. We see not six separate lines, but
three sets of two lines
 Continuity; we perceive smooth, continuous patterns rather than discontinuous
ones. This pattern could be a series of alternatives semicircles, but we perceive It
as two continuous lines- one way, one straight
 Closure; we fill in gaps to create a complete, whole object. Thus, we assume that
the circles on the left are complete but partially blocked by the (illusory) triangle.
Add nothing more than little line segments to close off the circles and your brain
stops constructing triangles
b) Depth Perception
DEPTH PERCEPTION: the ability to see objects in three dimensions although the
images that strike the retina are two-dimensional; allows us to judge distance
VISUAL CLIFF: a laboratory device for testing depth perception in infants and young
animals
 Biological maturation predisposes us to be wary of heights and experience amplifies
that fear
i. Binocular Cues
BINOCULAR CUES: depth cues, such as retinal disparity, that depend on the use of
two eyes
 The greater the retinal disparity, or difference between the two images, the closer the
object
RETINAL DISPARITY: a binocular cue for perceiving depth: By comparing images
from the retinas in the two eyes, the brain computes distance- the greater the disparity
(difference) between two images, the closer the object
ii. Monocular Cues
MONOCULAR CUES: depth cues, such as interposition and linear perspective,
available to either eye alone
 Relative Height; we perceive objects higher in our field of vision as farther away
 Relative Motion; As we move, objects that are actually stable may appear to
move
 Relative Size; if we assume two objects are similar in size, most people perceive
the one that casts the smaller retinal image as farther away
 Linear Perspective; Parallel lines appear to meet in the distance. The sharper the
angle of convergence, the greater the perceived distance
 Interposition; If one object partially blocks our view of another, we perceive it as
closer
 Light & Shado